LMZ23605TZ National Semiconductor, LMZ23605TZ Datasheet - Page 15

• Manufacturer Part Number: LMZ23605TZ
• Description: POWER MODULE, 36V, 5A, 7TO-PMOD
• Manufacturer: National Semiconductor

Specifications of LMZ23605TZ

• Primary Input Voltage: 36V
• No. Of Outputs: 1
• Output Voltage: 6V
• Output Current: 5A
• Voltage Regulator Case Style: TO-PMOD
• No. Of Pins: 7
• Operating Temperature Range: -40°C To +125°C
• Rohs Compliant: Yes

Whereas the falling threshold level can be calculated using:
V
R
OUTPUT VOLTAGE SELECTION
Output voltage is determined by a divider of two resistors
connected between V
vider is connected to the FB input.
The regulated output voltage determined by the external di-
vider resistors R
V
Rearranging terms; the ratio of the feedback resistors for a
desired output voltage is:
R
These resistors should generally be chosen from values in the
range of 1.0 kΩ to 10.0 kΩ.
For V
rectly and R
output load.
A table of values for R
plified applications schematic on page 2.
SOFT-START CAPACITOR SELECTION
Programmable soft-start permits the regulator to slowly ramp
to its steady state operating point after being enabled, thereby
reducing current inrush from the input supply and slowing the
output voltage rise-time.
Upon turn-on, after all UVLO conditions have been passed,
an internal 1.6mSec circuit slowly ramps the SS/TRK input to
implement internal soft start. If 2 mSec is an adequate turn–
on time then the Css capacitor can be left unpopulated.
Longer soft-start periods are achieved by adding an external
capacitor to this input.
Soft start duration is given by the formula:
t
This equation can be rearranged as follows:
C
SS
EN
O
ENH
FBT
SS
= 0.796V * (1 + R
= V
(falling) = V
= t
/ R
O
)
REF
SS
= 0.8V the FB pin can be connected to the output di-
FBB
* 50μA / 0.796V (5)
* C
= (V
FBB
SS
EN
FBT
O
can be set to 8.06kΩ to provide minimum
/ Iss = 0.796V * C
(rising) – 21 µA ( R
/ 0.796V) - 1 (3)
and R
FBT
O
FBT
and ground. The midpoint of the di-
/ R
FBB
, and R
FBB
is:
) (2)
FBB
SS
, is included in the sim-
/ 50uA (4)
ENT
|| 2 meg || R
ENTB
Enable input detail
FIGURE 1.
+
15
Using a 0.22μF capacitor results in 3.5 msec typical soft-start
duration; and 0.47μF results in 7.5 msec typical. 0.47 μF is a
recommended initial value.
As the soft-start input exceeds 0.796V the output of the power
stage will be in regulation and the 50 μA current is deactivat-
ed. Note that the following conditions will reset the soft-start
capacitor by discharging the SS input to ground with an in-
ternal current sink.
• The Enable input being pulled low
• Thermal shutdown condition
• Internal Vcc UVLO (Approx 4.3V input to V
TRACKING SUPPLY DIVIDER OPTION
The tracking function allows the module to be connected as
a slave supply to a primary voltage rail (often the 3.3V system
rail) where the slave module output voltage is lower than that
of the master. Proper configuration allows the slave rail to
power up coincident with the master rail such that the voltage
difference between the rails during ramp-up is small (i.e.
<0.15V typ). The values for the tracking resistive divider
should be selected such that the effect of the internal 50uA
current source is minimized. In most cases the ratio of the
tracking divider resistors is the same as the ratio of the output
voltage setting divider. Proper operation in tracking mode dic-
tates the soft-start time of the slave rail be shorter than the
master rail; a condition that is easy satisfy since the C
is replaced by R
for the power up interval of the master supply; once the SS/
TRK rises past 0.8V the input is no longer enabled and the 50
uA internal current source is switched off.
TKB
. The tracking function is only supported
30116909
IN
)
www.national.com
SS
cap